U.S. patent number 4,577,845 [Application Number 06/569,217] was granted by the patent office on 1986-03-25 for hydrostatic pressure xy table.
This patent grant is currently assigned to Citizen Watch Co., Ltd.. Invention is credited to Toshikazu Hatsuse, Sosaku Kimura.
United States Patent |
4,577,845 |
Kimura , et al. |
March 25, 1986 |
Hydrostatic pressure XY table
Abstract
A hydrostatic pressure XY table comprising first and second
sliding tables mounted on a bed. The two sliding tables are driven
perpendicularly to each other by separate motors through a first
lead screw supported on the bed and a second lead screw supported
on the first sliding table. The bed has a first trapezoidal groove
and the first sliding table has a second trapezoidal groove running
perpendicular to the first trapezoidal groove. The first sliding
table is engaged with the first trapezoidal groove and the second
sliding table is engaged with the second trapezoidal groove. Four
hydrostatic pressure guides are provided in the bed, to engage with
engaging surfaces of the first sliding table. Four hydrostatic
pressure guides are also provided in the first sliding table to
engage with engaging surfaces of the second sliding table. A
plurality of fluid pressure lines are provided for supplying
hydrostatic pressure to the engaging surfaces of the first and
second sliding tables. A hydrostatic pressure feed mechanism
consisting of a lead screw, a nut and a fluid pressure line for
supplying hydrostatic pressure through the nut to opposite screw
faces of the lead screw is provided for each sliding table. By use
of the hydrostatic pressure XY table it is possible to carry out
machining operations in which close dimensional tolerances must be
observed as in the grinding of magnetic disk heads and the grinding
and polishing of plastic shaping dies.
Inventors: |
Kimura; Sosaku (Saitama,
JP), Hatsuse; Toshikazu (Saitama, JP) |
Assignee: |
Citizen Watch Co., Ltd. (Tokyo,
JP)
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Family
ID: |
26339202 |
Appl.
No.: |
06/569,217 |
Filed: |
January 9, 1984 |
Foreign Application Priority Data
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Jan 18, 1983 [JP] |
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58-5279 |
Mar 8, 1983 [JP] |
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58-36667 |
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Current U.S.
Class: |
269/73; 108/137;
74/441; 74/89.33 |
Current CPC
Class: |
B23Q
1/0027 (20130101); B23Q 1/38 (20130101); B23Q
1/621 (20130101); Y10T 74/19902 (20150115); Y10T
74/18656 (20150115) |
Current International
Class: |
B23Q
1/26 (20060101); B23Q 1/62 (20060101); B23Q
1/38 (20060101); B23Q 1/25 (20060101); B23Q
1/00 (20060101); B23Q 001/18 () |
Field of
Search: |
;269/73,71 ;108/137,143
;74/441,424.8R,89.15 ;33/1M ;250/442.1,492.2 ;408/91 ;378/208 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2112676 |
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Sep 1971 |
|
DE |
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2731706 |
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Jan 1978 |
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DE |
|
25979 |
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Mar 1978 |
|
JP |
|
Primary Examiner: Schmidt; Frederick R.
Assistant Examiner: Schad; Steven P.
Attorney, Agent or Firm: Koda and Androlia
Claims
We claim:
1. In an XY table comprising a bed, a first lead screw supported on
the bed by bearings, a first motor provided on the bed for
rotatingly driving the first lead screw, a first sliding table
mounted on the bed for sliding motion in the X direction, the first
sliding table having a first nut for engagement with the first lead
screw, a second lead screw supported on the first sliding table by
bearings, a second motor provided on the first sliding table for
rotatingly driving the second lead screw, and a second sliding
table mounted on the first sliding table for sliding motion in the
Y direction, the second sliding table having a second nut for
engagement with the second lead screw, the improved hydrostatic
pressure XY table characterized in that the bed has a first
trapezoidal groove; the first sliding table is engaged with the
first trapezoidal groove and has a second trapezoidal groove
running perpendicular to the first trapezoidal groove; the second
sliding table is engaged with the second trapezoidal groove; four
hydrostatic pressure guides are provided in the bed, one on either
inclinded lateral wall of the first trapezoidal groove and one on
either side of the first trapezoidal groove on the upper surface of
the bed, to engage with engaging surfaces of the first sliding
table; four hydrostatic pressure guides are provided in the first
sliding table, one on either inclined lateral wall of the second
trapezoidal groove and one on either side of the second trapezoidal
groove on the upper surface of the first sliding table, to engage
with engaging surfaces of the second sliding table; a plurality of
fluid pressure lines are provided for supplying hydrostatic
pressure from an external hydrostatic fluid pressure source to the
engaging surfaces of the first and second sliding tables, each of
the fluid pressure lines for supplying hydrostatic fluid pressure
from an external hydrostatic fluid pressure source to engaging
surfaces of the first and second sliding tables comprises a
pantograph fluid pressure line consisting of a first rotatable
member on whichever of the base and the first sliding table
constitutes the stationary side and connected with the external
hydrostatic fluid pressure source, a second rotatable member fixed
on whichever of the first sliding table and the second sliding
table constitute the moving side, and a rotatable coupling provided
with a fluid passage for connecting the first member with the
second member, the pantographic fluid pressure line being disposed
within the area of the bed as viewed from the top and within the
space between the bed and first sliding table or between the first
sliding table and the second sliding table; a first hydrostatic
pressure feed mechanism consisting of the first lead screw, the
first nut and a fluid pressure line for supplying hydrostatic
pressure through the first nut to opposite screw faces of the first
lead screw is provided for the first sliding table; and a second
hydrostatic pressure feed mechanism consisting of the second lead
screw, the second nut and a fluid pressure line for supplying
hydrostatic pressure through the second nut to opposite screw faces
of the second lead screw is provided for the second sliding
table.
2. A hydrostatic pressure XY table according to claim 1, wherein
the engaging surfaces of the first sliding table opposed to the
inclined lateral walls of the first trapezoidal groove and to the
upper surfaces of the bed on both sides of the first trapezoidal
groove and the engaging surfaces of the second sliding table
opposed to the inclined lateral walls of the second trapezoidal
groove and to the upper surfaces of the first sliding table on both
sides of the second trapezoidal groove are each provided with one
or more rows of hydrostatic presure pockets.
3. A hydrostatic pressure XY table according to claim 1, wherein
each of the first and second nuts comprises a nut housing and two
female screws inserted and fixed within the nut housing to oppose
each other, the nut housing and the female screws being provided
with fluid pressure lines through which hydrostatic pressure is
supplied to one screw face of the associated lead screw through one
female screw and to the other screw face thereof through the other
female screw.
4. A hydrostatic pressure XY table according to claim 3, wherein a
spacer is provided between at least one of the female screws and
the nut housing for adjusting the lead face gap between the female
screw and the lead screw.
5. A hydrostatic pressure XY table according to claim 1, wherein
each of the first and second lead screws is provided with a
completely closed loop servo-mechanism comprising an optical scale
and a detector for detecting a signal from the optical scale, the
signal being fed back to the associated motor after being
electrically processed.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydrostatic pressure XY table suitable
for use in ultra-high precision machining, more particularly to a
hydrostatic pressure XY table optimally suited for use, for
example, in grinding the track surface of a magnetic head for a
magnetic disk unit and the beveled surface contiguous with this
track surface or in grinding a shaping die for plastic lenses.
2. Description of the Prior art
FIG. 1 of the attached drawings shows the configuration of a
ferrite core 1 of a magnetic head. In the fabrication of a magnetic
head employing such a ferrite core there is required a level of
grinding precision and quality considerably higher than in general
applications. This can be attriubuted to the following factors:
(1) The track width H determined by the two beveled surfaces
contiguous with the track surface 2 is very small and must be
machined with high dimensional precision and within very strict
tolerance limits.
(2) The surface to be machined consists of a hard, brittle material
like ferrite.
(3) The finished surface must be of high quality.
This type of machining work is generally carried out by grinding or
lapping. Because of the brittle nature of the material that has to
be machined, however, even the slightest vibration of the grinder
etc. used for the operation is liable to cause chipping of the
machined surface and it is thus necessary to assure high precision
rotation of the grinding tool and to feed the work with utmost
smoothness free from the influence of any irregularities on the
guide surfaces.
In the ordinary XY table there are used sliding or rolling guide
surfaces. The first of these is susceptible to sticking and
slipping during low-velocity feeding while the latter tends to give
rise to minute table vibration during travel of the rollers.
Moreover, the nut which engages with the lead screw in the
conventional XY table has either an acme or bore screw thread.
These are also disadvantageous since the acme screw thread has a
friction problem and the bore screw thread has poor damping
capacity and a tendency to generate minute vibration. As a result,
with the XY tables used up to now chipping of the material being
machined and other defects have been common.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide a
hydrostatic pressure XY table which is optimally suited for use in
the high-precision, high-quality machining of a brittle
material.
Another object of the invention is to provide such a hydrostatic
pressure XY table which is capable of precision positioning to
within 0.1 micron.
Still another object of the invention is to provide such a
hydrostatic pressure XY table having rigidity and damping capacity
adequate for withstanding machining load.
Still another object of the invention is to provide such a
hydrostatic pressure XY table which is able to carry out smooth and
steady feed even at extremely low velocities.
In accordance with the present invention there is provided a
hydrostatic pressure XY table comprising a bed having a first
trapezoidal groove; a first sliding table engaged with the first
trapezoidal groove and having a second trapezoidal groove running
perpendicular to the first trapezoidal groove; a second sliding
table engaged with the second trapezoidal groove; four hydrostatic
pressure guides provided in the bed, one on either inclined lateral
wall of the first trapezoidal groove and one on either side of the
first trapezoidal groove on the upper surface of the bed, to engage
with engaging surfaces of the first sliding table; four hydrostatic
pressure guides provided in the first sliding table, one on either
inclined lateral wall of the second trapezoidal groove and one on
either side of the second trapezoidal groove on the upper surface
of the first sliding table, to engage with engaging surfaces of the
second sliding table; a plurality of fluid pressure lines for
supplying hydrostatic pressure from an external hydrostatic fluid
pressure source to the engaging surfaces of the first and second
sliding tables; a first hydrostatic pressure feed mechanism for the
first sliding table consisting of a first lead screw and a first
nut engaged therewith, the first nut having a fluid pressure line
for supplying hydrostatic pressure to opposite screw faces of the
first lead screw; and a second hydrostatic pressure feed mechanism
for the second sliding table oriented perpendicular to the first
hydrostatic pressure feed mechanism consisting of a second lead
screw and a second nut engaged therewith, the second nut having a
fluid pressure line for supplying hydrostatic pressure to opposite
screw faces of the second lead screw.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to an embodiment
thereof shown in the attached drawings wherein:
FIG. 1 is a perspective view of a magnetic head for a magnetic disk
unit shown as one example of a workpiece to be machined by a
machine employing the hydrostatic pressure XY table according to
the present invention.
FIG. 2 is a perspective view showing the overall structure of a
hydrostatic pressure XY table according to one embodiment of the
present invention.
FIG. 3 is a plan view of the hydrostatic pressure XY table.
FIG. 4 is a cross-sectional view taken along line A--A in FIG.
3.
FIG. 5 is a cross-sectional view taken along line B--B in FIG.
3.
FIGS. 6(A) and 6(B) are a plan view and a cross-sectional view of a
specific structure for a fluid pressure line according to this
invention, FIG. 6(B) showing only the essential portions
thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a first sliding table 20 is mounted on a
base 10 having a first trapezoidal groove in such manner as to be
guided by the inclined lateral surfaces 10a, 10b of the first
trapezoidal groove and by the upper surfaces 10c, 10d of the base
10 located one on either side of the first trapezoidal groove. That
is to say, the first sliding table 20 is guided by four surfaces of
the base 10. At each engagement region between the bed 10 and the
first sliding table 20 is provided one or more rows of hydrostatic
pressure pockets 20a, 20b, 20c and 20d. A fluid delivered under
pressure from an external hydrostatic fluid pressure source (not
shown) passes through a fluid pressure line (not shown) in the bed
10, a pantograph fluid pressure line 11 adapted to expand and
contract with the travel of the first sliding table 20 and a fluid
pressure line 20e in the table to be supplied to the hydrostatic
pressure pockets 20a, 20b, 20c and 20d. As a result, a hydrostatic
bearing force is generated at each of the surfaces 10a, 10b, 10c
and 10d.
On the other hand, a first lead screw 18 is supported by
hydrostatic bearing 15, 16 and 17 provided in the bed 10 and is
rotatingly driven by a motor 13 through a speed reducer 14. Static
pressure is supplied to the opposite screw faces of the first lead
screw 18 via a fluid pressure line in the bed 10, a pantograph
fluid pressure line 12, a fluid pressure line 20f in the first
sliding table 20 and a fluid pressure line 21a in a first nut
housing 21. The nut housing 21 is provided with female screws 22,
23 having fluid pressure lines 22a, 23a, respectively. The female
screws 22, 23 engage with the first lead screw 18. Moreover, a pair
of hydrostatic pressure nuts are inserted and fixed within the
first nut housing 21 as opposed to each other. Since the screw
surfaces are supported by hydrostatic pressure through this
hydrostatic pressure feed mechanism, the rigidity and damping
capacity in the feed direction is improved and, further, it is made
possible to transfer smooth feeding motion to the first sliding
table 20 without friction or backlash.
The spacer 124 shown in the drawings is for adjusting the lead face
gap between the lead screw 18 and the female screws 22, 23. Fluid
exhausted from the aforesaid engagement regions passes through
exhaust passages 10e etc. to be once recovered in the first
trapezoidal groove in the bed 10 and is then exhausted to the
exterior of the bed 10.
The reliability of the first sliding table is further enhanced by a
completely closed loop servo-mechanism wherein a signal detected
from an optical scale 101 is detected by a detector 102 and then
after being electrically processed is fed back to the motor 13.
In a similar manner, a second lead screw 29 is rotatingly driven
via a speed reducer 25 by a second motor 24 fixed on the first
sliding table 20. The second lead screw 29 is supported on the
first sliding table 20 by hydrostatic bearings 26, 27 and 28.
Static pressure is supplied to the opposite screw faces of the
second lead screw 29 via the pantograph fluid pressure line 12, a
pantograph fluid pressure line 30, a fluid pressure line 32f in the
second sliding table 32, a fluid pressure line 33a in a second nut
housing 33, and fluid pressure lines 34a, 35a. A pair of female
screws 34, 35 are inserted and fixed within the second nut housing
33 as opposed to each other. A spacer 36 is provided between the
female screw 35 and the second nut housing 33. Thus the screw
surfaces are also supported by hydrostatic pressure by the second
hydrostatic pressure nut.
The first sliding table 20 is also provided with a trapezoidal
groove and the second sliding table 32 is mounted on the first
sliding table 20 in such manner as to be guided by the inclined
lateral surfaces 20g, 20h of this second trapezoidal groove and by
the upper surfaces 20i, 20j of the first sliding table 32 located
one on either side of the second trapezoidal groove. That is to
say, the second sliding table 32 is guided by four surfaces of the
first sliding table 20. At each engagement region between the first
sliding table 20 and the second sliding table 32 is provided one or
more rows of hydrostatic pressure pockets 32a, 32b, 32c and 32d. A
fluid delivered under pressure passes through the pantograph fluid
pressure line 11, a pantograph pressure fluid line 31 and a fluid
pressure line 32e in the second sliding table 32 to be supplied to
the hydrostatic pressure pockets 32a, 32b, 32c and 32d. As a result
a hydrostatic bearing force is generated at each of the surfaces
20g, 20h, 20i and 20j.
Moreover, the second sliding table 32 is also provided with a
completely closed loop servo-mechanism wherein there is provided an
optical scale 201 and the output signal of a detector 202 is fed
back to the motor 24. Thus, the second sliding table 32 can be fed
with the same high precision and high rigidity as the first sliding
table 20.
When the hydrostatic pressure XY table according to this invention
is applied to a machine tool it becomes possible to realize a
dramatic improvement in dimensional and positional accuracy as well
as in the quality of the machined surface in such operations as the
grinding of magnetic disk heads where a dimensional tolerance of
.+-.1 micron must be observed in the respective processing steps,
the grinding and polishing of plastic shaping dies where very
strict precision requirements must be observed regarding shaping
accuracy and surface roughness, and the machining of precision
index plates and optical communication connectors where extremely
high pitch precision is required.
As shown in FIG. 3 the hydrostatic pressure XY table according to
the embodiment shown in the drawings comprises four pantograph
fluid pressure lines as expandable and contractable means for
supplying hydrostatic pressure. These four pantograph fluid
pressure lines being all of the same structure, the description
here will be limited to the one denoted by reference numeral 11 and
shown in overall plan view in FIG. 6(A) and in a vertical
cross-sectional view of its essential portion in FIG. 6(B).
Fluid delivered under pressure from an external fluid pressure
source (not shown) passes through a fluid pressure line in the bed
10 and enters an inlet passage 40a formed in a pillar member 40. To
facilitate its attachment to the bed 10, the pillar member 40 is
provided with a screw portion 40b and a hexagonal nut portion 40c
and by means of these portions is tightly screwed into threaded
hole provided in the bed 10 so as to preclude any leakage of the
fluid.
A ring 41 having a pipe 43 fixed thereto by welding or the like is
fitted over one portion of the pillar member 40 so as to be free to
rotate thereabout. A seal member 42 is provided so as to prevent
leakage of the fluid as when the ring 41 rotates on the pillar
member 40.
On the table 20 is provided a pillar member 50 and related members
which are so similar in construction to those described above that
no detailed explanation will be given here. The ends of the pipes
43 and 49 opposite those fixed to the rings 41, 51 respectively
have attached thereto by welding or the like rings 45, 46. The
rings 45, 46 are fitted over a shaft 44 formed with a fluid
pressure passage 44a so as to be free to rotate thereabout. Seals
47, 48 are provided so as to constitute a leak proof coupling
member for the passage of fluid.
As the pantograph fluid pressure line constructed as described
above makes it possible to effectively utilize the space existing
between the bed 10 and the first sliding table 20, for example, it
can be used, as in the hydrostatic XY table of this embodiment, to
provide a highly compact unit.
The structure described in the foregoing is also very advantageous
from a practical viewpoint in that the fluid pressure lines do not
strike against or hinder the movement of other members and do not
obstruct the movement of the sliding tables so that it is possible
to prevent any damage to the hydrostatic pressure guide surfaces
which might occur should any of the fluid lines be damaged.
When expandable and contractable fluid pressure lines of the
foregoing type are incorporated into the hydrostatic pressure XY
table described above and the combination is applied to a machine
tool it becomes possible to stably carry out feed of the sliding
tables at a positioning precision of within 0.1 micron and to carry
out smooth and steady feed even at extremely low velocities. As a
result, it is possible to realize a dramatic improvement in
dimensional and positional accuracy as well as in the quality of
the machined surface in such operations as the grinding of magnetic
disk heads where a dimensional tolerance of .+-.1 micron must be
observed in the respective processing steps, the grinding and
polishing of semiconductor wafers where very strict precision
requirements must be observed regarding dimensional accuracy and
surface roughness, the grinding and polishing of shaping dies for
plastic optical components, and the machining of precision index
plates and optical communication connectors where extremely high
pitch precision is required.
The pantograph fluid pressure lines used in this invention are not
limited to the particular structure described with respect to the
foregoing embodiment, and any type of pantograph fluid pressure
lines may be used insofar as they are able to expand and contract
in response to the movement of the sliding tables and provide the
same function as the type described above.
Also, although the pantograph fluid pressure line mentioned above
has been described with reference to a hydrostatic pressure XY
table, it is by no means limited to such an application.
As will be clear from the foregoing description, when the
hydrostatic pressure XY table according to this invention is
applied to a machine tool it becomes possible to realize a dramatic
improvement in dimensional and positional accuracy as well as in
the quality of the machined surface in such operations as the
grinding of magnetic disk heads where a dimensional tolerance of
.+-.1 micron must be observed in the respective processing steps,
the grinding and polishing of plastic shaping dies where very
strict precision requirements must be observed regarding shaping
accuracy and surface roughness, and the machining of precision
index plates and optical communication connectors where extremely
high pitch precision is required.
* * * * *